In electrophotography (also known as xerography, electrophotographic imaging or electrostatographic imaging), the surface of an imaging member (e.g., photoreceptor) is first uniformly electrostatically charged. The imaging member contains a photoconductive insulating layer on a conductive layer and is then exposed to a pattern of activating electromagnetic radiation, such as a light. Charge generated by the photoactive pigment moves under the force of the applied field. The movement of the charge through the photoreceptor selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image. This electrostatic latent image is then developed to form a visible image by depositing oppositely charged particles on the surface of the photoconductive insulating layer.
The resulting visible image is then transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as a transparency or paper sheet. The imaging process may be repeated many times with reusable imaging members. The visible toner image is therefore transferred on the print substrate and is usually fixed or fused to form permanent images since the visible toner image is in a loose powdered form and can be easily disturbed or destroyed. The use of thermal energy for fixing toner images onto a support member is well known. In order to fuse electroscopic toner material onto a support surface permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be firmly bonded to the support.
Several approaches to thermal fusing of electroscopic toner images have been described in the prior art. These methods include providing the application of heat and pressure substantially concurrently by various means: a roll pair maintained in pressure contact; a belt member in pressure contact with a roll; and the like. Heat may be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure and contact time is provided. The balancing of these parameters to bring about the fusing of the toner particles is well known in the art, and they can be adjusted to suit particular machines or process conditions.
Fuser and fixing rolls or belts may be prepared by applying one or more layers to a suitable substrate. Typically, fuser and fixing rolls or belts include a surface layer for good toner releasing. Cylindrical fuser and fixer rolls may be prepared by applying a silicone elastomer or fluoroelastomer to serve as a releasing layer. Known fuser surface coatings also include crosslinked fluoropolymers such as VITON-GF® (DuPont) used in conjunction with a release fluid.
Another type of surface layer materials includes fluororesin such as polytetrafluoroethylene (PTFE), perfluoroalkylvinylether copolymer (PFA) and the like. This type of materials are desired for oil-less fusing, namely, no release fluid being required. Specifically, the Teflon surface enables oil-less fusing and the silicone layer provides conformability which enables rough paper fix, low mottle and good uniformity. Problems arise, however, due to insufficient mechanical robustness of the Teflon surface coatings, e.g., cracking and abrasion, which results in short operating life of the fuser. In addition, there is a need for electrical conductivity to dissipate the electrostatic built up during fusing process.
Carbon nanotubes (CNTs) possess exceptional mechanical properties and superior electric and thermal properties and can be used as reinforcement for structural composites. It is therefore desired to employ carbon nanotubes for the fuser. However, due to the unique structural features of CNTs, e.g., the nanometer size and the high aspect ratio, CNTs tend to stay aggregated in the resulting composite.
Thus, there is a need to overcome these and other problems of the prior art and to provide coating compositions and methods for making and using the coating compositions where CNTs can be stably and uniformly dispersed in the composition.